Confirmatory Assay to Find Inhibitors of T. brucei phosphofructokinase: Counter Screen against Bacillus PFK
Various species of the protozoan family Trypanosomatidae are responsible for a range of serious human diseases in tropical and subtropical areas of the world. The subspecies Trypanosoma brucei is one of three known to cause sleeping sickness in sub-Saharan Africa, significantly contributing to the millions of people worldwide who are infected by these parasites and endangering hundreds of millions more. Many of the disorders caused by trypanosomatids are fatal if left untreated, but most currently used drugs are inefficient and toxic. ..more
Various species of the protozoan family Trypanosomatidae are responsible for a range of serious human diseases in tropical and subtropical areas of the world. The subspecies Trypanosoma brucei is one of three known to cause sleeping sickness in sub-Saharan Africa, significantly contributing to the millions of people worldwide who are infected by these parasites and endangering hundreds of millions more. Many of the disorders caused by trypanosomatids are fatal if left untreated, but most currently used drugs are inefficient and toxic.
Of many possible drug targets in trypanosomatid parasites, the carbohydrate metabolism pathway is seen as potentially one of the most selective, as T. brucei, when in the bloodstream of its mammalian host, is entirely dependent on the conversion of the blood sugar glucose into pyruvate for its ATP supply . Oxidative metabolism involving the mitochondrial tricarboxylic acid cycle and oxidative phosphorylation are repressed in these parasites, and recent RNA interference (RNAi) experiments have shown that even partial depletion of certain individual glycolytic enzymes can lead to the death of cultured parasites . One such glycolytic enzyme, phosphofructokinase (PFK), catalyzes the formation of fructose-1,6-bisphosphate (F1,6BP) and ADP from fructose-6-phosphate (F6P) and ATP, and in many metabolic circumstances makes an important contribution to the control of flux through the glycolytic pathway. As a specific glycolytic target, PFK is particularly attractive as it catalyzes the first irreversible step in glycolysis, and structural and kinetic studies have shown very substantial and essential differences from corresponding host enzymes , allowing for the discovery of parasite-selective inhibitors.
A luminescent biochemical assay was performed that used luciferase-based nucleotide detection (ADP-Glo, Promega) to examine the effect of identified actives against a bacterial isoform of PFK, namely Bacillus stearothermophilus, for target specificity. The assay is identical in concept to the T. brucei PFK qHTS assay, but instead uses the B. stearothermophilus isoform of PFK (Sigma, St. Louis, MO) and ATP/F6P at bacterial isoform-specific Km concentrations.
NIH Chemical Genomics Center [NCGC]
NIH Molecular Libraries Probe Centers Network [MLPCN]
MLPCN Grant: MH092153-01
Assay Submitter (PI): Malcom Walkinshaw, University of Edinburgh
Substrate buffer was dispensed into white, solid 1536-well plates at 3 uL/well in 0.1M triethanolamine (TEA) buffer, pH 8.0, containing final concentrations of 5 mM MgCl2, 0.01% Tween20, 0.6 mM fructose-6-phosphate (F6P) and 0.1 mM ATP. Then, 23 nl of compounds or DMSO were delivered to each well using a pin tool. One uL of B. stearothermophilus PFK (0.1 M TEA, 0.01% Tween20, 0.1% bovine serum albumin (BSA) and 10 nM PFK, final concentrations) was then dispensed, and plates were incubated at room temperature for 45 min. The luminescent detection reagent, ADP-Glo (Promega), was then added in two steps: the first reagent, ADP-Glo (which converts remaining uncatalyzed ATP), was added at 2.5 uL/well and incubated for ten minutes at room temperature, and the second component, Kinase Detection reagent (which converts ADP to ATP as a substrate for luciferase-based luminescence), was added immediately after at 5uL/well, followed by one final ten minute room temperature incubation. The plates were measured on a ViewLux plate reader for luminescent signal using a clear filter with a one second exposure. The %Activity was determined from the corrected luminescence values. 1x (1.25nM) and 0x PFK enzyme controls (untreated) were included to normalize %Activity of identified inhibitors; 0x enzyme values corresponded to 100%Activity (full inhibition), while 1x PFK enzyme values were used to normalize 0% Activity (no inhibition).
1. Compounds are first classified as having full titration curves, partial modulation, partial curve (weaker actives), single point activity (at highest concentration only), or inactive. See data field "Curve Description". For this assay, apparent inhibitors are ranked higher than compounds that showed apparent activation.
2. For all inactive compounds, PUBCHEM_ACTIVITY_SCORE is 0. For all active compounds, a score range was given for each curve class type given above. Active compounds have PUBCHEM_ACTIVITY_SCORE between 40 and 100. Inconclusive compounds have PUBCHEM_ACTIVITY_SCORE between 1 and 39. Fit_LogAC50 was used for determining relative score and was scaled to each curve class' score range.
* Activity Concentration. ** Test Concentration.
Data Table (Concise)